Surprisingly，one thing that rarely works is mouthwash.The liquid can mask bad breath smell with its own smell，but the effect lasts no more than an hour.Some mouthwashes claim to kill the bacteria responsible for bad breath.The trouble is，they don’t necessarily reach all offending germs.Most bacteria are well protected from mouthwash under thick layers of mucus (粘液)．If the mouthwash contains alcohol—as most do—it can worsen the problem by drying our mouth.

　　1．Which of the following is right?

　　A．Saliva flow gradually increases with age.

　　B．Alcohol drinking does good to bad breath.

　　C．Mouthwash is not an effective way to bad breath.

　　D．Mouth bacteria can’t grow fast in airless conditions.

　　2．Which of the following is mentioned as one of the causes of bad breath?

　　A．Tooth trouble. B．Sulfur rich food.

　　C．Too much exercise.D．Mental pressure.

　　3．According to the passage，alcohol has something to do with bad breath mainly because________.

　　A．it keeps offending bacteria from reproducing

　　B．its smell adds to bad breath

　　C．it kills some helpful bacteria

　　D．it affects the normal flow of saliva

　　4．Mouthwashes are not an effective cure for bad breath mainly because________.

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